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172

ABSORPTION OF NITROUS GASES

culty of securing cheap materials for construction gave the
square tower an .economic advantage, that difficulty is no
longer present, and consequently the round tower is almost
universally adopted.

Ratio of Diameter to Height. The shape of cross section
of the tower has also a considerable bearing on the ratio of
diameter to height, since difficulties of gas and liquid distribu-
tion, which may be inconsiderable with a tower of small
diameter, are magnified considerably as the diameter of the
tower is increased. It is a matter of experience that when an
ordinary gravity feed of liquid enters the top of an absorption
tower, it is not until a distance of several feet down that the
whole of the packing is homogeneously wetted. In conse-
quence, a certain amount of the tower space is not utilized.
It is well known also that the wider the tower, the more
difficult is it to secure good distribution of the absorbing liquid.
Some kind of constant-level overflow apparatus has to be used,
with all its cumulative defects due to accumulation of grit
and dirt, etc., while in addition it is inevitable that channelling '
will take place to a very increased extent. This has been the
experience of most users of towers of diameter greater than
12-15 feet. Careful consideration should be given, therefore,
to the question of limiting the diameter of the tower to a
maximum of 10 feet. It is also evident that, even with a good
packing, the gas entering the tower at a point in the circum-
ference will be drawn up the tower for some distance before it
is spread homogeneously over the tower. The wider the tower,
the greater will be the " dead " space so produced.

For efficient working, therefore, it is advisable that the ratio

of---------should not exceed 4 to 1. At Notodden the towers

height

are 20 feet diameter and 70 feet high, as already stated. In
this connection it should be mentioned that the American
nitrate plant at Alabama had absorption towers 60 feet high
and 13 feet square for handling approximately 1,600 tons of
HN03 per week. The Badische Anilin und Soda Fabrik at
Oppau and Leverkusen use two brick, two granite, and two
steel towers (for alkaline absorbents), 80 feet x 20 feet,
80 feet x 30 feet, and 80 feet x 15 feet respectively, to recover
approximately 2,000 tons of HN03 per week. Meister Lucius

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